Dandy. That's the left bank of the engine. Most likely those codes did not all set at the same time. The Engine Computer can detect a single cylinder misfire, of which you have three, and it can detect a multiple cylinder misfire, which it did not. Multiple cylinder misfires occur at the same time and will be related to something they have in common such as a bad sensor reading, low fuel pressure, contaminated fuel, or a vacuum leak.
A single cylinder misfire is caused by something that is related to just that one cylinder such as the spark plug, plug wire, injector, or burned valve. Given the nature of the codes, (multiple single cylinder misfires), I'd start by looking at a combination of those generalizations. That means multiple items related to a single cylinder. A perfect example would be high-mileage spark plugs and wires. A worn spark plug will cause random misfires in one cylinder, but just as two tires wear out at the same rate, so does a set of spark plugs.
If the left front oxygen sensor incorrectly reports a rich condition, the Engine Computer will reduce the pulse width to all four injectors on that bank. It can't tell which cylinder is running rich. It can only adjust the mixture to all four cylinders together. That could result in misfires from a fuel / air mixture that is too lean.
That oxygen sensor could also be responding correctly. O2 sensors do not detect unburned fuel, only oxygen, but some of the normal oxygen in the exhaust will be burned with that extra fuel before it reaches the sensor. The sensor will take longer than normal to detect the lean part of the cycle. In this case, a leaky injector would be suspect. Assuming the computer is reducing fuel to the entire left side of the engine which is resulting in the misfires, suspect the injector for cylinder number 7 which is not misfiring.
If spark plugs and wires don't solve the problem, consider switching the injector from cylinder number 7 with one on the passenger side to see if the misfires go to the other side.
Saturday, February 5th, 2011 AT 8:04 PM